Most permanent hair coloring products contain a pigment, developer and an alkalizing agent. The developer is usually an oxidizing agent such as hydrogen peroxide in water or a cream lotion. The alkalizing agent is most often ammonia or an ammonia substitute that causes the hair to swell.
Chemicals found in synthetic hair dyes, including ammonia, lead, and/or coal tar, are toxic and can have dangerous side-effects such as hair loss, burning, redness, itchy skin, swelling, or trouble breathing. Many people forego hair coloring to avoid exposure to the chemicals found in the coloring compositions.
Hair colorants that are classified as “direct dyes” do not require further chemical modification in the coloring process. In contrast to “oxidation dyes”, which color hair by oxidation of a dye precursor during the coloring process, direct dyes do not require a chemical oxidant in the coloring composition. For example, acid dyes are direct dyes that accomplish hair coloring by forming an ionic bond between the dye and a positively-charged amino acid residue within the hair shaft. However, this ionic bond is typically cleaved when hair is shampooed, resulting in the dye being released from the hair.
Because direct dyes are generally not retained in or on the hair shaft (and, if used as hair colorants, are readily washed out of the hair), mechanisms which enhance direct dye uptake and retention are needed. If a chemical such as ammonia is used to swell the hair cuticle, direct dye penetration and retention in the hair shaft is still quite low.
A chemical fixative (such as a metal-containing mordanting agent) can increase retention of a direct dye on hair strands. However, traditional compositions containing a fixative may cause sensitization or allergic reactions in some individuals. Fixatives and corresponding hair coloring methods also often contain heavy metal or aluminum ions, some of which have been linked to neurological and other disorders. Some fixative formulations contain siloxanes which) can be toxic, persistent, and bio-accumulative. Most also contain organic solvents, which present flammability hazards and can have an undesirable drying effect on the hair.
There is a current need for a benign and effective method of enhancing dye uptake and retention on hair, which avoids the use of chemical oxidants, fixatives, mordanting agents, bleaching or swelling agents, and other substances that may cause undesired health effects.